Method for the repair of a compressor rotor designed in blisk technology

ABSTRACT

With a method for the repair of compressor rotors designed in blisk technology the damaged stage is severed from the rotor, and a new blisk is joined to the rotor by electron-beam welding. For stress relieving the rotor is subjected to local thermal treatment by means of a current produced in the weld area by electro-magnetic induction.

This application claims priority to German Patent Application DE 10 2006033 299.7 filed Jul. 17, 2006, the entirety of which is incorporated byreference herein.

This invention relates to a method for the repair of a compressor rotordesigned in blisk technology and having a plurality of blisks joined toform a one-piece assembly in which a severely damaged stage is replacedby a new one and the rotor is subsequently subjected to thermaltreatment.

On gas turbine engines, as is generally known, compressors are usedwhich include several rotor stages which are joined to form a one-pieceassembly and are each designed in blisk technology, with the rotorblades being integral with the disk. Severely damaged blades or bladeportions are usually cut off and replaced by new repair elementsattached in a welding process. In order to reduce the stresses producedin the weld-near area, the entire compressor drum, or only theinternally stressed weld zone of the repaired blade, must be subjectedto thermal treatment. Thermal treatment of the entire compressor may,however, result in distortion of the latter, entailing costly mechanicalrework. Also, previously removed coatings must be re-applied and thesurface re-hardened. For performance of a local heat treatment confinedto the respective weld area, costly capsule techniques are knownpreventing the non-damaged parts of the blisk from being heated.

Since effort and cost for the repair of severely damaged compressors isparticularly high in connection with a local thermal treatment, one orseveral of the blisks joined to each other by welding are in this caseremoved, or severed, from the compressor and replaced by new blisksfitted in a welding process. In this case, the compressor having severalblisks joined to each other by welding must, however, be subjected tothermal treatment in a furnace which leads to the disadvantagesdescribed above.

In a broad aspect, the present invention provides for a significantreduction of the work effort for the repair of severely damagedcompressors.

It is a particular object of the present invention to provide animproved method for construction and repair in accordance with thefeatures described herein. Useful developments of the invention will beapparent from the present description.

The essential idea of the present invention is that a new blisk iselectron-beam welded to the compressor rotor as replacement for thedestroyed blisk (or during new construction) and that both the weld andthe confined adjacent zones affected by the weld heat are subjected to astress-relieving treatment using inductively generated heat. Theinduction parameters can be set such that the current induced into thecomponent for heat generation is actually confined to the welding areaand the temperature required for stress relieving is produced in thisarea only. Coatings previously applied to the compressor rotor need notbe stripped prior to thermal treatment and, therefore, not be re-appliedin a subsequent process. Re-treatment of the blades for surfacehardening is similarly not required. Finally, localized thermaltreatment provides for minimum distortion of the rotor, as a result ofwhich the otherwise required costly mechanical rework will similarly nolonger be necessary, or only to a lesser extent. Locally confinedgeneration of heat enables the repair process to be repeated morefrequently. The heat required for the thermal treatment is producedlocally peripherally along the weld joint.

The method is applicable to both the repair and the manufacture of bliskrotors. Advantageous here are the dispensability of the cost-intensivethermal treatment of an entire rotor assembly in a furnace and therapidity of the local thermal treatment which is even integratable intothe welding process.

This invention is more fully described in the light of a preferredembodiment.

On a compressor whose rotor is constructed from blisks joined to eachother and features a plurality of damaged blades in a stage, theaffected blisk is severed from the compressor drum and replaced by a newdisk with integral blades (blisk) which is joined to the compressor drumby electron-beam welding. Upon welding the replacement disk to thecompressor rotor (rotor subassembly), only the weld joint and the areasadjacent to the weld joint which are strongly heated in the weldingprocess are subjected to local thermal treatment by inductive heating,in that a current is induced into the weld joint and a confinedbi-lateral area of the rotor using a magnetic field produced on theperiphery of the joint, thus generating the temperature required forthermal treatment of the material. The parameters for the locallyconfined thermal treatment can be well set so that the compressor rotorwill generally distort only slightly and rework due to thermaldistortion will not be necessary, or to a minor extent only.Furthermore, surface re-coating necessary after furnace heat treatmentof the entire rotor and/or surface re-hardening, for example by glassbead peening, of the non-locally heat-treated areas is now obsolete.Upon thermal treatment, inspection of the weld joint and, if applicable,mechanical rework in the weld joint area is performed. The method isapplicable to all compressor rotors, both in blisk and conventionaltechnology (disk/blade).

1. A method for the repair of a compressor rotor designed in blisktechnology and having a plurality of blisks joined to form a one-pieceassembly in which a severely damaged stage is replaced by a new one andthe rotor is subsequently subjected to thermal treatment, wherein thenew blisk is joined to the rotor by electron-beam welding and only aweld joint and an area adjacent to the weld joint which has beenaffected by a heat of the weld is subjected to local thermal treatmentby a current produced in this area by electro-magnetic induction.
 2. Amethod in accordance with claim 1, wherein the thermal treatment iseffected locally, peripherally along the weld joint.
 3. A method inaccordance with claim 1, wherein the weld joint is inspected andsubjected to mechanical rework, if necessary.
 4. A method for themanufacture of blisk rotors designed in blisk technology and havingblisks joined to form a one-piece assembly, wherein a further blisk isjoined to a rotor sub-assembly by electron-beam welding and only a weldjoint and an area adjacent to the weld joint which has been affected bya heat of the weld is subjected to local thermal treatment by a currentproduced in this area by electromagnetic induction.
 5. A method for themanufacture of compressor rotors constructed of multiple componentsjoined together to form a one-piece assembly, wherein a furthercomponent is joined to a rotor sub-assembly by electron-beam welding andonly a weld joint and an area adjacent to the weld joint which has beenaffected by a heat of the weld is subjected to local thermal treatmentby a current produced in this area by electro-magnetic induction.